1. Field of the Invention
This invention relates to an apparatus for producing flake particles, and more particularly, to an apparatus for carrying out the art of producing flake particles by projecting a stream of molten metallic material upon the rotating or moving surface of a heat extracting member and thereby extracting the heat from the molten material so as to solidify the metallic material into a large number of flake particles. The solidified flakes are then removed from the heat extracting member by means of centrifugal force imparted thereto by the rotation of the heat extracting member.
2. Description of the Prior Art
Heretofore, various kinds of flake particle making apparatus have been made which produce flake particles by contacting molten metal with the rotating surface of a heat extracting member and allowing the molten metal to solidify thereon.
The most typical invention known to the inventor of this application is U.S. Pat. No. 4,215,084.
According to this patent, the heat extracting member is constructed as a rotating drum, upon the outer surface of which a continuing stream of molten material is projected. The outer rotating surface of the drum is constructed with a number of serrations formed substantially parallel to the axis of rotation of the rotating drum. When a continuing thin stream of molten metal is projected upon the surface of these serrations, the heat contained in the metal is extracted by the serrations, resulting in solidification of the metal into a large number of flake particles.
Accordingly, if it is required to increase the production rate of flake particles by carrying out the process in parallel, it becomes necessary to lengthen each rotating drum and to provide a plurality of nozzles. However, it is also demanded to effect fine and correct adjustment of the nozzle opening to obtain flake particles as fine and as equal in size as possible. Such adjustment not only encounters technical difficulties, but a fine nozzle opening also results in problems with respect to service life, process control and costs.
Since such metal flake particles are most generally mixed into plastics for use as electromagnetic interference shielding materials, it is also required that the flake particles be capable of being uniformly dispersed and mixed.
However, flake particles produced by such conventional apparatus contain a considerable amount of deformed particles or smaller sized particles. Further, the particles were generally made square in shape which thereby obstructs uniform mixing and dispersion of such particles in plastic material.
The main cause for bringing about such a nonuniformity in the size and shape of the particles is due to the fact that the serrated surface of the heat extracting member is higher at the rear part of each upper surface serration than at the front part with respect to the direction of the rotation of the rotating member. Thus, the molten metal is liable to be repelled or shed which hinders a smooth transferring of the molten metal onto the heat extracting member.
Typical prior art apparatus for obtaining fine solidified metal particles are disclosed in U.S. Pat. Nos. 3,710,842, 3,838,185, 3,896,203, 3,904,344 and 3,908,745. However, all of these prior art inventions relate to methods or apparatus for producing filaments or fibers; although the aforesaid patents have a common feature with regard to the fact that high production efficiency can be performed with a low cost.